Wireless communication apparatus and wireless communication method

ABSTRACT

To suppress concentration of channel quality information requests and reports in a case of discontinuously transmitting reference signals at specific resources in a time domain, and thereby preventing degradation in throughput. A transmission apparatus transmits an instruction of CSI request distributed for each reception apparatus in a subframe concurrently with or earlier than a reference signal CSI-RS to each of reception apparatuses. Each of the reception apparatuses detects the CSI request from the transmission apparatus and calculates CSI from a channel estimation value of CSI-RS received thereafter. Then, the reception apparatus identifies CSI report subframe of the own apparatus from CSI report interval information of a given time interval notified in advance, the subframe in which the CSI request is detected and transmission timing of CSI-RS, and transmits a feedback signal including CSI report value by using PUSCH at the timing of the CSI report subframe.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/167,691 filed May 27, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/573,901 filed Dec. 17, 2014, which is acontinuation of U.S. patent application Ser. No. 14/044,618 filed Oct.2, 2013, which is a continuation of U.S. patent application Ser. No.13/375,437 filed on Nov. 30, 2011, which is a national-stage entry ofInternational Application No. PCT/JP2010/003030 filed on Apr. 27, 2010,the contents of which are incorporated herein by reference.

BACKGROUND Technical Field

The present invention relates to a wireless communication apparatus anda wireless communication method which can be applied to a wirelesscommunication system, such as a cellular system.

Description of the Related Art

In a wireless communication system, such as a cellular system, areference signal is introduced to obtain various indexes of apropagation channel and a transmission signal. For example, LTE (LongTerm Evolution) of a next-generation communication system which isstudied in the 3GPP (3rd Generation Partnership Project) as theinternational standards organization of mobile communication uses areference signal (RS). In downlink communication from a base station toa user equipment, a reference signal which is transmitted from atransmission apparatus (base station) to a reception apparatus (userequipment) is mainly used for (1) estimation of a propagation channelfor demodulation, (2) quality measurement for frequency scheduling andadaptive MCS (Modulation and Coding Scheme) control, and the like. Inthe LTE, a reference signal is transmitted in a predetermined unit ofwireless resources in a multi-antenna system for applying MIMO (MultipleInput Multiple Output).

In LTE-advanced (hereinafter, referred to as LTE-A) which is a moreadvanced communication system than LTE, in order to achieve high-speedperformance, the introduction of high-order MIMO (for example, eighttransmission antennas), coordinated multiple-point transmission andreception (CoMP), or the like is studied. For this reason, in additionto a reference signal (first reference signal) which is studied in LTE,an additional reference signal (second reference signal) for LTE-A isneeded, and a transmission method thereof is discussed.

For example, as described in Non-Patent Literature 1, in LTE-A, twotypes of reference signals are studied for the above-described purposes.

(1) Demodulation RS: for PDSCH (Physical Downlink Shared Channel)demodulation, and specific to user equipment (UE) (UE-specific) withapplication of the number of layers same as PDSCH and precoding.

(2) CSI-RS: for CSI (Channel State Information) measurement, (examplesof CSI include CQI (Channel Quality Indicator), PMI (Precoding MatrixIndicator), RI (Rank Indicator), channel matrix, channel covariancematrix, interference component, and the like), and specific to a cell(cell-specific) with no application of precoding. Examples of specificchannel quality information include CQI corresponding to a combinationof a predefined modulation scheme and code rate, PMI which selects aprecoding matrix based on a current channel condition from a predefinedcodebook, RI corresponding to the desired number of transmission links,a channel matrix in which the fading value of a MIMO channel isexpressed in a matrix, a channel covariance matrix in which thecomponents of the channel matrix are used in a channel covariancematrix, an interference component obtained by subtracting a desiredsignal from a reception signal, and the like.

However, the purposes are not exclusively positioned. Specifically, adiscussion proceeds assuming that the CSI-RS may be used for the purpose(1).

In LTE, the minimum unit of frequency scheduling and adaptive MCScontrol is defined as a resource block (RB, and hereinafter, referred toas RB) in a frequency domain and as a subframe in a time domain. Thesignal configuration of one subframe or RB (hereinafter, referred to as1 RB/subframe) as a resource unit is made such that a control signal anda reference signal RS are allocated from the head of the time axis, anddata is subsequently allocated. The reference signal RS is allocated ina specific OFDM symbol and a specific subcarrier of the 1 RB/subframe.As an example of the CSI-RS transmission method for LTE-A, a method isknown in which a CSI-RS (second reference signal) for 8 antennas istransmitted only in a specific RB/subframe, and a 4 antennas-compliant4RS (first reference signal) for LTE is transmitted in anotherRB/subframe (for example, see Non-Patent Literature 2).

In the CSI-RS transmission method, a configuration is made such that anLTE user equipment compatible with only LTE can receive data at aresource which does not transmit the CSI-RS, and the 4RS for LTE istransmitted at a resource of a specific RB/subframe, allowing the LTEuser equipment to perform CSI measurement. Since the RB/subframe inwhich the CSI-RS for 8 antennas is transmitted is arranged discretely,it is possible to perform CSI measurement with satisfactory accuracy ateach resource by interpolation/averaging between the resources.

The need for discontinuously transmitting a CSI-RS as a reference signalin the above-described manner will be described. CSI-RS transmissionsignificantly adversely affects an LTE user equipment compatible onlywith an existing system. Specifically, if a rule is provided tomultiplex a resource transmitting a CSI-RS to only an allocated resourceof an advanced system-compliant user equipment (hereinafter, referred toas an LTE-A user equipment), there is a restriction on scheduling withrespect to the LTE user equipment. If such a rule is not provided, asignal which cannot be recognized from the LTE user equipment on the LTEuser equipment-allocated resource is multiplexed, causing degradation ofdemodulation performance in the user equipment. Since any phenomenondescribed above is not preferable, a solution is made such that CSI-RStransmission is limited at a specific time resource focusing onresources in the time domain. That is, it is necessary todiscontinuously transmit the CSI-RS, instead of transmitting the CSI-RSin continuous subframes.

An example of a procedure of a channel quality information (CSI)request, CSI measurement and report will be described with reference toFIG. 30. FIG. 30 is an operation explanatory diagram showing a procedureof a channel quality information request and a report in response to thechannel quality information request in LTE. Here, description will beprovided assuming communication between a base station (eNB: evolvedNode-B) and a user equipment (UE) in a cellular mobile communicationsystem.

The base station (eNB) transmits a cell-specific reference signal(cell-specific RS: CRS) in each subframe. When an instruction for a CSIrequest is indicated to a user equipment (UE1 or UE2), the base stationsends a notification to the user equipments using a downlink controlchannel PDCCH (Physical Downlink Control Channel). Here, as an operationexample of the user equipment, the behavior of a first user equipmentUE1 will be described. If an own apparatus-addressed CSI request isdetected by the PDCCH, UE1 performs CSI measurement using the CRS of thesubframe, and reports CSI to the base station using an uplink datachannel PUSCH (Physical Uplink Shared Channel) after a predefined numberof subframes (in this case, 4 subframes). The base station performsuplink resource allocation assuming a PUSCH subframe for a CSI reportfrom the user equipment, and indicates a request by the PDCCH. In thebase station, an uplink signal from UE1 is received in accordance withthe PDCCH which indicates the request and the content of the CSI reportis detected. The base station realizes frequency scheduling of downlinkdata and adaptive MCS control using the obtained CSI.

The reasons for defining the number of subframes from the CSI request tothe CSI report include a reason from the viewpoint of the CSI report dueto the amount of processing in the user equipment, and a reason from theviewpoint of the utilization of CSI when the scheduler of the basestation which receives the CSI report utilizes the relevant information.For the former reason due to the amount of processing in the userequipment, it is necessary that CSI measurement is performed after theCSI request is received, the amount of processing necessary forencoding/modulating the relevant information to generate a signal istaken into consideration, and a processing time equal to or greater thana given time is provided for realization with no large load.Accordingly, it is necessary to define the number of subframes equal toor greater than a given time as a requirement from the viewpoint of theCSI report.

For the latter reason from the viewpoint of the utilization of CSI,processing is performed for allocating the resource of each userequipment on the basis of the reported CSI information. Thus, takinginto consideration the efficiency of resource allocation, it ispreferable that there is a slight change between the actual allocationtime and the CSI measurement time. However, in a wireless propagationenvironment, as the time elapses, the change in CSI increases due totime-dependent fading. For this reason, as the requirement from theviewpoint of the utilization of CSI, it is necessary to set a subframewithin a given time in which the efficiency of resource allocation isnot significantly degraded. The number of subframes from the CSI requestto the CSI report is determined such that the requirements from the twoviewpoints are compatible.

The same discussion is established as to a reference signal at the timeof uplink communication from a user equipment to a base station. InLTE-A, the introduction of a technique, such as MIMO, is studied inwhich multiple transmission systems (antennas and transmissionamplifiers) are provided in a user equipment, and it is necessary totransmit a reference signal for frequency scheduling and adaptive MCScontrol using multiple transmission systems. Thus, the expansion of asounding RS (SRS) which is one of the reference signals for use in LTEin compliant with multiple transmission systems is studied. For example,as described in Non-Patent Literature 3, a method is studied in which anSRS is transmitted from a user equipment at an indicated timing inaccordance with a request from a base station. With regard to SRStransmission in LTE, similarly to the need for discontinuoustransmission in CSI-RS, the SRS can be transmitted and received once ata set interval T_(sfc) of the base station LTE such that an adverseeffect on data transmission of the user equipment is minimized.

CITATION LIST Non-Patent Literature

-   Non-Patent Literature 1: 3GPP TSG RAN WG1 #56, R1-091066, CATT,    CMCC, Ericsson, Huawei, LGE, Motorola, Nokia, Nokia Siemens    Networks, Nortel, Panasonic, Philips, Qualcomm Europe, Samsung,    Texas Instruments, “Way forward on downlink reference signals for    LTE-A”, Feb. 9-13, 2009-   Non-Patent Literature 2: 3GPP TSG RAN WG1 #56, R1-090619, Samsung,    “DL RS Designs for Higher Order MIMO”, Feb. 9-13, 2009-   Non-Patent Literature 3: 3GPP TSG RAN WG1 #59, R1-094653, Nokia    Siemens Networks, Nokia, “Channel sounding enhancements for    LTE-Advanced”, Nov. 9-13, 2009

BRIEF SUMMARY Technical Problem

However, in the above-described transmission method whichdiscontinuously transmits a CSI-RS, the following problem occurs. FIG.31 is an operation explanatory diagram illustrating a problem in aCSI-RS transmission method in which a CSI-RS is discontinuouslytransmitted. For the higher advancement of a communication system, it isassumed that a reference signal (CSI-RS) for channel qualitymeasurement, such as CoMP or high-order MIMO, is discontinuouslytransmitted. In this case, since it is necessary to coordinate thetransmission timing of a reference signal as a measurement target withthe timing at which an instruction of a CSI request is indicated, CSIrequests concentrate in a specific subframe from the base station eNB tothe user equipments UE1 and UE2. Accordingly, a CSI request is indicatedto a plurality of user equipments simultaneously, and it is necessary togenerate a corresponding PDCCH in the relevant subframe. For thisreason, the PDCCH which is a finite resource is consumed, making itdifficult to allocate downlink data to the relevant subframe. Thus, thethroughput of downlink data in the relevant subframe is degraded. Asdescribed above, since CSI reports are simultaneously sent from the userequipments UE1 and UE2 to the base station eNB after a predefined numberof subframes from the CSI request, a corresponding uplink resource inthe relevant subframe is consumed. For this reason, it becomes difficultto allocate uplink data to the relevant subframe, causing degradation inthroughput of uplink data.

In the above-described transmission method which sets an SRS subframeonly at a specific interval, the following problem occurs. FIG. 32 is anoperation explanatory diagram illustrating a problem in an SRStransmission method which sets an SRS subframe only at a specificinterval. It is necessary to coordinate the transmission timing of areference signal as a measurement target with the timing at which an SRSinstruction is indicated, SRS instructions concentrate in a specificsubframe from the base station eNB to the user equipments UE1 and UE2.Accordingly, an SRS instruction is indicated to a plurality of userequipments simultaneously, and it is necessary to generate acorresponding PDCCH in the relevant subframe. For this reason, the PDCCHwhich is a finite resource is consumed, making it difficult to allocatedownlink data to the relevant subframe. Thus, the throughput of downlinkdata in the relevant subframe is degraded. As described above, since SRSare simultaneously transmitted from the user equipments UE1 and UE2 tothe base station eNB after a predefined number of subframes from the SRSinstruction, a corresponding uplink resource in the relevant subframe isconsumed. For this reason, it becomes difficult to allocate uplink datato the relevant subframe, causing degradation in throughput of uplinkdata.

The present invention has been achieved in consideration of theabove-described situation, and an object of the invention is to providea wireless communication apparatus and a wireless communication methodcapable of suppressing concentration of channel quality informationrequests and reports in a case of discontinuously transmitting referencesignals at specific resources in a time domain, and thereby preventingdegradation in throughput.

Solution to Problem

The invention provides, as a first aspect, a wireless communicationapparatus, including: a reference signal generator that is configured togenerate a reference signal for allowing a reception apparatus servingas a communication party to calculate a channel quality of atransmission channel; a channel quality information request settingsection that is configured to set a transmission timing of a channelquality information request for causing channel quality information withrespect to the reference signal to be fed back from the receptionapparatus so that timings are set to be temporally distributed over theplurality of reception apparatuses simultaneously with or before atransmission timing of the reference signal to be discontinuouslytransmitted on the time axis; a channel quality information reportsetting section that is configured to set a transmission timing of achannel quality information report to be transmitted from the receptionapparatus in response to the channel quality information request so thata report interval is set to a given time interval as a time intervalfrom transmission of the channel quality information request totransmission of the channel quality information report from thereception apparatus; and a communication section that is configured totransmit the reference signal and the channel quality informationrequest, and receive the channel quality information report.

The invention includes, as a second aspect, the wireless communicationapparatus, wherein the channel quality information report settingsection is configured to set the report interval to be a time intervalobtained by adding a predetermined offset to a time interval necessaryfrom reception of the reference signal to transmission of the channelquality information report in the reception apparatus.

The invention includes, as a third aspect, the wireless communicationapparatus, wherein the channel quality information report settingsection is configured to set the predetermined offset to be a valuecorresponding to the number of reception apparatuses under the wirelesscommunication apparatus.

The invention includes, as a fourth aspect, the wireless communicationapparatus, the channel quality information report setting section isconfigured to set the report interval to be a time interval matched witha retransmission interval at the time of communication with thereception apparatus.

The invention includes, as a fifth aspect, the wireless communicationapparatus, including a report interval information notification sectionthat is configured to notify the reception apparatus of report intervalinformation which indicates the report interval.

The invention includes, as a sixth aspect, the wireless communicationapparatus, wherein the channel quality information report settingsection is configured to instruct a timing, at which the channel qualityinformation report is transmitted from the reception apparatus servingas the communication party, to the communication section, and thecommunication section is configured to receive the channel qualityinformation report at the indicated timing.

The invention includes, as a seventh aspect, the wireless communicationapparatus, including a resource allocation section that is configured toallocate resources regarding communication from the wirelesscommunication apparatus to the reception apparatus and communicationfrom the reception apparatus to the wireless communication apparatus onthe basis of the transmission timing of the channel quality informationrequest and the transmission timing of the channel quality informationreport.

The invention provides, as an eighth aspect, a wireless communicationapparatus, including: a channel quality calculator that is configured tocalculate a channel quality of a transmission channel on the basis of areference signal discontinuously transmitted on the time axis receivedfrom a transmission apparatus serving as a communication party; afeedback information generator that is configured, when one of channelquality information requests transmitted at timings temporallydistributed over a plurality of reception apparatuses including thewireless communication apparatus is received from the transmissionapparatus simultaneously with or before a transmission timing of thereference signal, to generate feedback information including a channelquality information report which indicates the calculated channelquality on the basis of a preset report interval which is a given timeinterval from transmission of the channel quality information request totransmission of the channel quality information report in response tothe channel quality information request; and a communication sectionthat is configured to receive the reference signal and the channelquality information request, and transmit the channel qualityinformation report.

The invention includes, as a ninth aspect, the wireless communicationapparatus, wherein the feedback information generator is configured togenerate the feedback information including the channel qualityinformation report on the basis of a time interval, set as the reportinterval, obtained by adding a predetermined offset to a time intervalnecessary from reception of the reference signal to transmission of thechannel quality information report.

The invention includes, as a tenth aspect, the wireless communicationapparatus, wherein the feedback information generator is configured togenerate the feedback information including the channel qualityinformation report on the basis of a time interval, set as the reportinterval, matched with a retransmission interval at the time ofcommunication with the transmission apparatus.

The invention provides, as an eleventh aspect, a wireless communicationbase station apparatus, including any one of the wireless communicationapparatus.

The invention provides, as a twelfth aspect, a wireless communicationmobile station apparatus including any one of the wireless communicationapparatus.

The invention provides, as a thirteenth aspect, a wireless communicationmethod in a wireless communication apparatus, the wireless communicationmethod including: generating a reference signal for allowing a receptionapparatus serving as a communication party to calculate a channelquality of a transmission channel; when setting transmission timing of achannel quality information request for causing channel qualityinformation with respect to the reference signal to be fed back from thereception apparatus, setting timings temporally distributed over aplurality of reception apparatuses simultaneously with or beforetransmission timing of the reference signal discontinuously transmittedon the time axis; when setting transmission timing of a channel qualityinformation report in response to the channel quality informationrequest to be transmitted from the reception apparatus, setting a reportinterval to be a given time interval as a time interval fromtransmission of the channel quality information request to transmissionof the channel quality information report from the reception apparatus;and transmitting the reference signal and the channel qualityinformation request, and receiving the channel quality informationreport.

The invention provides, as a fourteenth aspect, a wireless communicationmethod in a wireless communication apparatus, the wireless communicationmethod including: calculating a channel quality of a transmissionchannel on the basis of a reference signal discontinuously transmittedon the time axis received from a transmission apparatus serving as acommunication party; when one of channel quality information requestswhich are transmitted at timings temporally distributed over a pluralityof reception apparatuses including the wireless communication apparatusis received from the transmission apparatus simultaneously with orbefore the transmission timing of the reference signal, generatingfeedback information including a channel quality information reportwhich indicates the calculated channel quality on the basis of a presetreport interval which is a preset given time interval from transmissionof the channel quality information request to transmission of thechannel quality information report in response to the channel qualityinformation request; and transmitting the channel quality informationreport.

With the above-described configuration, the timing at which a channelquality information request is transmitted and the timing at which achannel quality information report is transmitted are respectivelydistributed. Thus, it is possible to distribute communication resourcesto be used for channel quality information requests in the time domain,and also to distribute communication resources to be allocated aschannel quality information reports. Therefore, it is possible tosuppress concentration of channel quality information requests andchannel quality information reports at specific resources in the timedomain, making it possible to prevent degradation in throughput.

Advantageous Effects of Invention

According to the invention, it is possible to provide a wirelesscommunication apparatus and a wireless communication method capable ofsuppressing concentration of channel quality information requests andreports in a case of discontinuously transmitting reference signals atspecific resources in a time domain, and thereby preventing degradationin throughput.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a main part of atransmission apparatus according to a first embodiment of the invention.

FIG. 2 is a block diagram showing the configuration of a main part of areception apparatus according to the first embodiment of the invention.

FIG. 3 is a diagram showing an operation relating to a CSI request and aCSI report in the first embodiment.

FIG. 4 is a block diagram showing the configuration of a main part of atransmission apparatus according to a second embodiment of theinvention.

FIG. 5 is a diagram showing an operation relating to a CSI request and aCSI report in the second embodiment.

FIG. 6 is a block diagram showing the configuration of a main part of atransmission apparatus according to a third embodiment of the invention.

FIG. 7 is a block diagram showing the configuration of a main part of areception apparatus according to the third embodiment of the invention.

FIG. 8 is a diagram showing an operation relating to a CSI request and aCSI report in the third embodiment.

FIG. 9 is a block diagram showing the configuration of a main part of atransmission apparatus according to a fourth embodiment of theinvention.

FIG. 10 is a block diagram showing the configuration of a main part of areception apparatus according to the fourth embodiment of the invention.

FIG. 11 is a diagram showing an operation relating to a CSI request anda CSI report in the fourth embodiment.

FIG. 12 is a block diagram showing the configuration of a main part of atransmission apparatus according to a fifth embodiment of the invention.

FIG. 13 is a block diagram showing the configuration of a main part of areception apparatus according to the fifth embodiment of the invention.

FIG. 14 is a diagram showing an operation relating to a CSI request anda CSI report in the fifth embodiment.

FIG. 15 is a block diagram showing the configuration of a main part of atransmission apparatus according to a sixth embodiment of the invention.

FIG. 16 is a block diagram showing the configuration of a main part of areception apparatus according to the sixth embodiment of the invention.

FIG. 17 is a diagram showing an operation relating to a CSI request anda CSI report in the sixth embodiment.

FIG. 18 is a table showing an example of a reference value of a CSIreport offset corresponding to a difference in path-loss informationbetween two cells in the sixth embodiment.

FIG. 19 is a block diagram showing the configuration of a main part of atransmission apparatus according to a seventh embodiment of theinvention.

FIG. 20 is a table showing an example of a reference value of an SRStransmission timing corresponding to a residual data quantity in theseventh embodiment.

FIG. 21 is a block diagram showing the configuration of a main part of areception apparatus according to the seventh embodiment of theinvention.

FIG. 22 is a diagram showing an operation relating to SRS instructionand SRS transmission in the seventh embodiment.

FIG. 23 is a block diagram showing the configuration of a main part of atransmission apparatus according to an eighth embodiment of theinvention.

FIG. 24 is a block diagram showing the configuration of a main part of areception apparatus according to the eighth embodiment of the invention.

FIG. 25 is a table showing an example of a reference value of an SRStransmission timing corresponding to surplus transmission power in theeighth embodiment.

FIG. 26 is a diagram showing an operation relating to SRS instructionand SRS transmission in the eighth embodiment.

FIG. 27 is a block diagram showing the configuration of a main part of atransmission apparatus according to a ninth embodiment of the invention.

FIG. 28 is a block diagram showing the configuration of a main part of areception apparatus according to the ninth embodiment of the invention.

FIG. 29 is a diagram showing an operation relating to SRS instructionand SRS transmission in the ninth embodiment.

FIG. 30 is an operation explanatory diagram showing a procedure of achannel quality information request and a report with respect to thechannel quality information request in LTE.

FIG. 31 is an operation explanatory diagram illustrating a problem in aCSI-RS transmission method which discontinuously transmits a CSI-RS.

FIG. 32 is an operation explanatory diagram illustrating a problem in anSRS transmission method which sets an SRS subframe only at a specificinterval.

DETAILED DESCRIPTION

Embodiments show an example where a wireless communication apparatus anda wireless communication method according to the invention are appliedto a cellular system for mobile communication, such as a mobile phone.Here, a case will be described where communication by MIMO is performedin a wireless communication system in which a base station (BS: alsocalled eNB) serves as a transmission apparatus and a user equipment (UE)of a mobile station serves as a reception apparatus. It is assumed thata base station performs communication with a user equipment compatiblewith LTE serving as a first communication system and a user equipmentcompatible with LTE-A serving as a second communication system. Therelationship between the first communication system (LTE) and the secondcommunication system (LTE-A) is established on the assumption that thesecond communication system is a communication system which accepts alarger number of transmission antennas on the reception side than in thefirst communication system. In this case, a reference signal forfrequency scheduling or adaptive MCS control is transmitted from thebase station to the user equipment. As the reference signal, in additionto a first reference signal 4RS for LTE (for 4 antennas), a secondreference signal CSI-RS for LTE-A (for 8 antennas) is used.

First Embodiment

In a first embodiment, a CSI request as a channel quality informationrequest is transmitted from a transmission apparatus to each receptionapparatus to be temporally distributed over a plurality of receptionapparatuses at the timing simultaneously with or earlier than thetransmission timing of a reference signal CSI-RS for measuring CSI. TheCSI request is a request which causes a CSI report value as a channelquality information report to be fed back from a reception apparatusserving as a communication party. Each reception apparatus calculatesCSI from the reference signal CSI-RS, and transmits the CSI report fromthe reception apparatus to the transmission apparatus at the timing whena CSI report interval which is a given time interval set in advanceelapses from the reception timing of the CSI request. The set value ofthe CSI report interval is a given subframe interval, and set inaccordance with, for example, the number of reception apparatuses whichperform communication, or the like, and is notified from thetransmission apparatus to the reception apparatus. Thus, the timing atwhich the CSI request is transmitted and the timing at which the CSIreport is transmitted respectively are distributed.

Next, the configuration of specific examples of a transmission apparatusand a reception apparatus in a wireless communication system of thisembodiment will be described.

FIG. 1 is a block diagram showing the configuration of a main part of atransmission apparatus according to a first embodiment of the invention.FIG. 2 is a block diagram showing the configuration of a main part of areception apparatus according to the first embodiment of the invention.

In this embodiment, it is assumed that wireless communication isperformed between the transmission apparatus shown in FIG. 1 and thereception apparatus shown in FIG. 2 using radio waves. Here, it isassumed that the transmission apparatus shown in FIG. 1 is applied to awireless communication base station apparatus (base station, BS, eNB) ofa cellular system, and the reception apparatus shown in FIG. 2 isapplied to a user equipment (UE) serving as a wireless communicationmobile station apparatus, such as a mobile phone. Here, it is assumedthat a MIMO system is configured in which wirelesstransmission/reception is performed using a plurality of antennas at thetime of both transmission and reception, the transmission apparatus canperform transmission to each of a plurality of reception apparatuses,and precoding transmission is performed such that a plurality ofantennas are weighted on the transmission side. As the form of acommunication signal, it is assumed that communication is performed by amulti-carrier communication method using an OFDM (Orthogonal FrequencyDivision Multiplexing) signal. As a specific example, a case will bedescribed where the base station serving as a transmission apparatusperforms communication with an LTE-compliant LTE user equipment and anLTE-A-compliant LTE-A user equipment serving as a reception apparatus.

The transmission apparatus shown in FIG. 1 includes a plurality of userequipment transmission signal processors 131 m and 131 n, anencoder/modulator 132, a precoding processor 133, a plurality oftransmission RF sections 134 a to 134 d and 134 e to 134 h, and aplurality of antennas 135 a to 135 d and 135 e to 135 h. Thetransmission apparatus also includes a scheduler 136, a CSI requestsetting section 137, a CSI-RS generator 138, an LTE 4RS generator 139, aCSI report interval setting section 140, and a downlink control signalgenerator 141. The transmission apparatus also includes a plurality ofuser equipment reception signal processors 151 m and 151 n, a receptionRF section 152, a separator 153, and a CSI report demodulator 154.

A radio wave which is transmitted from a counterpart apparatus (forexample, the reception apparatus shown in FIG. 2) is received by theantenna 135 a. A high-frequency signal of the radio wave received by theantenna 135 a is converted to a signal in a comparatively low frequencyband, such as a baseband signal, by the reception RF section 152, andthen input to the user equipment reception signal processors 151 m and151 n. The user equipment reception signal processors 151 m and 151 nperform signal processing on reception signals corresponding to the userequipments for LTE-A, LTE, and the like, and respectively have aseparator 153 and a CSI report demodulator 154. The separator 153separates a feedback signal from a reception signal, outputs a CQIreport in the feedback signal to the CQI report demodulator 154, andoutputs other reception signals to a demodulator/decoder (not shown).The CQI report in the feedback signal is demodulated in the CQI reportdemodulator 154 and input to the scheduler 136. The scheduler 136performs at least one of frequency scheduling and adaptive MCS controlas scheduling relating to a transmission signal on the basis of channelquality information CQI reported from the reception apparatus.

The user equipment transmission signal processors 131 m and 131 nperform signal processing on transmission signals corresponding to theuser equipment for LTE-A, LTE, and the like, and respectively have anencoder/modulator 132 and a precoding processor 133. Theencoder/modulator 132 performs encoding of transmission data,multiplexing of a control signal or the like, rate-matching,interleaving, modulation, or the like, and outputs the result to theprecoding processor 133. The precoding processor 133 performs weightingfor forming beams of transmission waves on transmission signals outputto a plurality of antennas, and outputs the transmission signals to thetransmission RF sections 134 a to 134 d and 134 e to 134 h of theantennas.

In the transmission RF sections 134 a to 134 d and 134 e to 134 h,processing, such as serial/parallel conversion or inverse Fouriertransform, is performed on the transmission signals. Then, thetransmission signals are converted to high-frequency signals in apredetermined radio frequency band, power-amplified, and thentransmitted from the antennas 135 a to 135 d and 135 e to 135 h as radiowaves. In the example of the figure, a transmitter for LTE-A generatestransmission signals which are transmitted using 8 antennas. Thetransmission signals from the transmission apparatus are transmitted tothe reception apparatuses as notification channels, control signals,data signals including various kinds of data, and the like. Thenotification channels and the control signals are transmitted asnondirective signals which do not form beams, and the data signals aretransmitted as directive signals which form predetermined beams based onbeam numbers by precoding in predetermined transmission channels.

The CSI request setting section 137 sets the CSI request transmissiontiming to each reception apparatus, and notifies setting information ofthe CSI request transmission timing to the CSI report interval settingsection 140 and each user equipment reception signal processor. The CSIrequest setting section 137 sends a notification to the scheduler 136 togenerate a control signal of a CSI request for UE in a subframe of theset CSI request transmission timing. The CSI report interval settingsection 140 sets a time interval (the number of subframes) from when aCSI request is transmitted until a CSI report is received (from when aCSI request of the own apparatus is transmitted until a CSI report of acommunication party apparatus is transmitted) as a CSI report intervalcorresponding to a report interval. In this case, an integer value whichis a value common to a plurality of reception apparatuses belonging tothe own apparatus is set. The CSI report interval setting section 140notifies the value of the set CSI report interval to each receptionapparatus regularly through a notification channel or the like. The CSIreport interval setting section 140 receives the setting information ofthe CSI request transmission timing from the CSI request setting section137 to each reception apparatus, and instructs a subframe, in which aCSI report determined on the basis of the set CSI report interval istransmitted, to the separator 153 of the relevant UE.

The separator 153 obtains the information of the CSI requesttransmission timing from the CSI request setting section 137, receivesthe value of the CSI report interval from the CSI report intervalsetting section 140, and recognizes the timing of a subframe in which aCSI report is transmitted from the relevant UE. The separator 153retrieves a CSI report from a reception signal in the relevant subframe,and outputs the CSI report to the CSI report demodulator 154.

The CSI-RS generator 138 generates a reference signal CSI-RS for LTE-A(for 8 antennas), and allocates CSI-RS at a resource corresponding tothe relevant transmission subframe. The LTE 4RS generator 139 generatesa reference signal 4RS for LTE (for 4 antennas), and allocates 4RS ateach resource. In the configuration example of FIG. 1, it is assumedthat CSI-RS is allocated at Ant#4 to Ant#7 (antennas 135 e to 135 h)with the intention of the application to high-order MIMO, and only thereference signal 4RS for LTE is allocated at Ant#0 to Ant#3 (antennas135 a to 135 d) and transmitted.

The scheduler 136 performs resource allocation of each user equipmentusing the channel quality information CQI received from the CSI reportdemodulator 154. The downlink control signal generator 141 generates adownlink control signal including allocation information of a downlinksignal on the basis of the allocation of each user equipment by thescheduler 136. Although the figure with the intention of the applicationto high-order MIMO has been described, CSI-RS transmission is notlimited thereto. Although an example has been described where 4 antennasare provided for LTE and additional 4 antennas are provided forhigh-order MIMO, the invention is not limited thereto. For example, 2antennas may be provided for LTE and additional 2 antennas may beprovided for high-order MIMO, a combination of both LTE and high-orderMIMO may be made, or 8 antennas in total of 2 antennas for LTE and 6antennas for high-order MIMO may be provided, or the like.

In the above configuration, the CSI-RS generator 138 realizes thefunctions of a reference signal generator. The CSI request settingsection 137 realizes the functions of a channel quality informationrequest setting section. The CSI report interval setting section 140realizes the functions of a channel quality information report settingsection. The user equipment signal processors 131 m and 131 n, thetransmission RF sections 134 a to 134 d and 134 e to 134 h, thereception RF section 152, the user equipment reception signal processors151 m and 151 n realize the functions of a communication section. Thescheduler 136 realizes the functions of a resource allocator.

The reception apparatus shown in FIG. 2 includes a plurality of antennas211 a and 211 b, a plurality of reception RF sections 212 a and 212 b, achannel estimator 213, a CSI calculator 214, a MIMO demodulator 215, aCSI request detector 216, a decoder 217, a CRC checker 218, a feedbackinformation generator 219, an encoder 220, a multiplexer 221, and atransmission RF section 222.

Radio waves which are transmitted from a counterpart apparatus (forexample, the transmission apparatus shown in FIG. 1) are received by aplurality of separate antennas 211 a and 211 b. A high-frequency signalof the radio wave received by the antenna 211 a is converted to a signalin a comparatively low frequency band, such as a baseband signal, by thereception RF section 212 a, and undergoes processing, such as Fouriertransform or parallel/serial conversion, to be converted to a receptionsignal of serial data. Similarly, a high-frequency signal of the radiowave received by the antenna 211 b is converted to a signal in acomparatively low frequency band, such as a baseband signal, by thereception RF section 212 b, and undergoes processing, such as Fouriertransform or parallel/serial conversion, to be converted to a receptionsignal of serial data. The outputs of the reception RF sections 212 aand 212 b are input to the channel estimator 213 and the MIMOdemodulator 215.

The channel estimator 213 performs channel estimation on the basis of areference signal in a signal transmitted from each transmission antennaof the counterpart apparatus (transmission apparatus), and calculates achannel estimation value. In this case, the reception apparatusspecifies the position of a reference signal for channel qualitymeasurement on the basis of control information separately notified fromthe transmission apparatus. Channel estimation is performed assumingthat a reference signal is allocated in a predefined OFDM symbol of therelevant resource and a subcarrier. The channel estimation valuecalculated by the channel estimator 213 is input to the CSI calculator214 and the MIMO demodulator 215.

The MIMO demodulator 215 performs demodulation on a reception signalcorresponding to the own apparatus (own reception apparatus) using thechannel estimation value received from the channel estimator 213, andoutputs the demodulated signal to the decoder 217. At this time,deinterleaving, rate-dematching, likelihood combining, and the like areperformed. The decoder 217 performs decoding on a signal input from theMIMO demodulator 215 to restore reception data. At this time,error-correction decoding is performed on a signal after MIMO separationreceived from the MIMO demodulator 215, and the result is output to theCRC checker 218. The CRC checker 218 performs error detection on asignal after decoding output from the decoder 217 through CRC (CyclicRedundancy Check) check, and outputs information regarding thepresence/absence of a data error indicating whether or not receptiondata after decoding includes an error to the feedback informationgenerator 219. Then, reception data is output from the CRC checker 218.

The CSI request detector 216 receives a demodulated signal output fromthe MIMO demodulator 215 as input, detects a CSI request signal, andnotifies the detection result to the CSI calculator 214. When a CSIrequest signal is detected by the CSI request detector 216, the CSIcalculator 214 calculates channel quality information (CQI, PMI, RI, andthe like) on the basis of the channel estimation value in the channelestimator 213, and outputs the result to the feedback informationgenerator 219 as a CSI report value.

The feedback information generator 219 generates feedback informationincluding the CSI report value calculated by the CSI calculator 214, andoutputs the feedback information to the multiplexer 221. At this time,the reception apparatus stores CSI report interval informationseparately notified from the transmission apparatus through anotification channel or the like in the feedback information generator219. The feedback information generator 219 generates a signal with theCSI report value received from the CSI calculator 214 as feedbackinformation in a subframe delayed by the CSI report interval set value.

If it is necessary to transmit the decoding result (Ack/Nack) ofdownlink data in the relevant subframe, the feedback informationgenerator 219 determines whether or not decoded reception data includesan error on the basis of the error detection result in the CRC checker218, and generates Ack/Nack information. If the decoding result does notinclude an error, Ack (Acknowledgement) is generated, and if thedecoding result includes an error, Nack (Negative Acknowledgement) isgenerated. The CSI report value and the Ack/Nack information aresynthesized and output to the multiplexer 221.

The encoder 220 performs encoding on transmission data and outputs theresult to the multiplexer 221. The multiplexer 221 performs multiplexingon a transmission signal including input feedback information, encodedtransmission data, and the like. Rate-matching for adaptively settingthe number of modulation multiple values or the code rate, interleaving,modulation, and the like are performed, and the result is output to thetransmission RF section 222. In the transmission RF section 222,processing, such as serial/parallel conversion or inverse Fouriertransform, is performed. Then, the transmission signal is converted to ahigh-frequency signal in a predetermined radio frequency band,power-amplified, and then transmitted from the antenna 211 a as a radiowave. At this time, the feedback information, such as the CSI reportvalue or the Ack/Nack information, which is transmitted from thereception apparatus is transmitted to the transmission apparatus as afeedback signal and reported.

In the above configuration, the channel estimator 213 and the CSIcalculator 214 realize the functions of a channel quality calculator.The feedback information generator 219 realizes the functions of afeedback information generator. The reception RF sections 212 a and 212b, the MIMO demodulator 215, the multiplexer 221, and the transmissionRF section 222 realize the functions of a communication section.

Next, the operations of the transmission apparatus and the receptionapparatus in the first embodiment will be described in detail. FIG. 3 isa diagram showing an operation relating to a CSI request and a CSIreport in the first embodiment. Here, a case will be described where aCSI request is transmitted from a base station (eNB) serving as atransmission apparatus to two user equipments (UE1 and UE2) serving as areception apparatus, and a CSI report is returned from each userequipment to the base station.

The transmission apparatus eNB sets the CSI report interval set valuen_(CSI-RS)+a as a value common to a plurality of reception apparatusesbelonging to the own apparatus in advance in the CSI report intervalsetting section 140. n_(CSI-RS) is the minimum required number ofsubframes from when CSI-RS is received until a CSI report is transmittedfor the reason from the viewpoint of a CSI report due to the amount ofprocessing in the user equipment, and ‘a’ is an offset value which isadded as a fixed value. The offset value ‘a’ is a value which can bechanged depending on the situation. For example, an integer value equalto or greater than 1 is determined by the number of user equipmentsserving as a reception apparatus under the base station at present. CSIreport interval information indicating the CSI report interval set valuen_(CSI-RS)+a is notified to each reception apparatus regularly through anotification channel or the like. In this case, the minimum requirednumber n_(CSI-RS) of subframes of the CSI report interval is known inthe reception apparatus through a prenotification from the transmissionapparatus. Thus, it should suffice that, for example, only the offsetvalue ‘a’ is notified from the transmission apparatus to the receptionapparatus through signaling. In addition to the offset value ‘a’, theCSI report interval set value n_(CSI-RS)+a, the minimum required numbern_(CSI-RS) of subframes, and the like may be notified.

The maximum value of the CSI report interval set value n_(CSI-RS)+a isset to be smaller than the transmission interval (for example, a10-subframes interval (10 msec interval)) of the reference signalCSI-RS. Similarly to the offset value ‘a’, the CSI report interval setvalue n_(CSI-RS)+a or the maximum value of the minimum required numbern_(CSI-RS) of subframes may be variably determined depending on thesituation of the user equipment serving as a reception apparatus, or thelike.

The transmission apparatus sets the transmission timing of the CSIrequest at the timing not overlapping between the reception apparatusesin the CSI request setting section 137, and performs scheduling ofresources for transmitting the reference signal CSI-RS and the CSIrequest in the scheduler 136. The user equipment transmission signalprocessor 131 m outputs an instruction of the CSI request to thereception apparatuses UE1 and UE2 to be distributed over the receptionapparatuses in a subframe at the timing simultaneously with or earlierthan the reference signal CSI-RS. The CSI request is notified to thereception apparatus using the downlink control channel PDCCH of therelevant timing. In this case, the transmission timing of the CSIrequest which is transmitted to each reception apparatus earlier thanCSI-RS is set such that the time interval from when the CSI request istransmitted until CSI-RS is transmitted is equal to or smaller than theoffset value ‘a’ of the CSI report interval set value n_(CSI-RS)+a.Thus, in each reception apparatus, it is possible to secure the minimumrequired number n_(CSI-RS) of subframes from when CSI-RS is receiveduntil the CSI report is transmitted.

A reception apparatus UE which meets the CSI request specifies a CSIreport subframe of the own apparatus from the CSI report intervalinformation notified previously, the subframe in which PDCCH includingthe CSI request is detected, and the transmission timing of CSI-RS. Asubframe when the CSI report interval set value n_(CSI-RS)+a elapsesfrom the subframe in which the own apparatus-addressed CSI request isdetected becomes the CSI report subframe. As a CSI report operation, thereception apparatus detects the CSI request from the transmissionapparatus in the CSI request detector 216, and calculates CSI from thechannel estimation value of CSI-RS received after CSI request detectionin the CSI calculator 214. In the feedback information generator 219, afeedback signal including the CSI report value is generated and outputat the timing of the specified CSI report subframe. The feedback signalincluding the CSI report value is reported to the transmission apparatususing the uplink data channel PUSCH of the relevant timing.

With the above-described operation, from the viewpoint of thetransmission apparatus eNB, it is possible to distribute the downlinkcontrol channel PDCCH for a CSI request in the time domain.Simultaneously, it is possible to distribute the resource of the uplinkdata channel PUSCH which is allocated as a CSI report.

As described above, in the first embodiment, the timing at which the CSIrequest is transmitted from the transmission apparatus to each receptionapparatus is distributed at the timing simultaneously with or earlierthan CSI-RS, and the CSI report is transmitted from each receptionapparatus to the transmission apparatus at the timing after a givensubframe interval set in advance from the reception timing of the CSIrequest. Therefore, it is possible to distribute the timing at which theCSI request is transmitted and the timing at which the CSI report istransmitted, thereby suppressing concentration of CSI requests and CSIreports at specific resources in the time domain and preventingdegradation in throughput.

Second Embodiment

In a second embodiment, the given CSI report interval set value in thefirst embodiment is set to be matched with a retransmission interval atthe time of communication between a transmission apparatus and areception apparatus in a wireless communication system. The transmissionapparatus transmits a CSI request to each reception apparatus to betemporally distributed simultaneously with or earlier than thetransmission timing of the reference signal CSI-RS for CSI measurement.Each reception apparatus calculates CSI from the reference signalCSI-RS, and transmits a CSI report to the transmission apparatus at thetiming when the CSI report interval set value elapses from the receptiontiming of the CSI request, that is, when the retransmission intervalelapses after the CSI request is received. Thus, the timing at which theCSI request is transmitted and the timing at which the CSI report istransmitted respectively are distributed.

FIG. 4 is a block diagram showing the configuration of a main part of atransmission apparatus according to a second embodiment of theinvention. In the figure, the same constituent elements as those in thefirst embodiment are represented by the same reference numerals.Description will be mainly provided focusing on portions different fromthe first embodiment, and description of the same portions will beomitted.

In the transmission apparatus of the second embodiment, the operationsof a CSI report interval setting section 440 and a scheduler 436 aredifferent from those in the first embodiment. The CSI report intervalsetting section 440 sets an integer value, which is a value common to aplurality of reception apparatuses belonging to the own apparatus, as aCSI report interval. The CSI report interval is set to be matched withthe retransmission interval in the wireless communication system. TheCSI report interval setting section 440 notifies the set value of theCSI report interval to each reception apparatus regularly through anotification channel or the like. The CSI report interval settingsection 440 notifies the scheduler 436 that the interval between a CSIrequest and a CSI report obtained by applying the CSI report intervalset value is matched with the retransmission interval of an uplink datasignal. The scheduler 436 regards an uplink resource, which is consumedby the CSI request and the CSI report, as a specific retransmissionprocess, and performs uplink data allocation positively using anirrelevant the retransmission process.

Next, the operations of the transmission apparatus and the receptionapparatus in the second embodiment will be described in detail. FIG. 5is a diagram showing an operation relating to a CSI request and a CSIreport in the second embodiment. Here, as in the first embodiment, acase will be described where a CSI request is transmitted from a basestation (eNB) serving as a transmission apparatus to two user equipments(UE1 and UE2) serving as a reception apparatus, and a CSI report isreturned from each user equipment to the base station.

The transmission apparatus eNB sets a CSI report interval set value,which is a value common to a plurality of reception apparatusesbelonging to the own apparatus, in advance in the CSI report intervalsetting section 440. Here, the CSI report interval set value is set to avalue (in the example of the figure, 8 subframes) matched with aretransmission interval at the time of communication between atransmission apparatus and a reception apparatus in a wirelesscommunication system. That is, the value is set such that the intervalbetween a CSI request and a CSI report obtained by applying the CSIreport interval set value is matched with the retransmission interval ofan uplink data signal. The transmission interval of the reference signalCSI-RS to be discontinuously transmitted is set to, for example, a10-subframes interval (10 msec interval). The configuration other thanthe CSI report interval set value is the same as in the firstembodiment. With the above-described operation, from the viewpoint ofthe transmission apparatus eNB, it is possible to distribute thedownlink control channel PDCCH for a CSI request in the time domain, andalso to distribute the uplink data channel PUSCH which is allocated as aCSI report.

According to the second embodiment, as in the first embodiment, it ispossible to suppress concentration of CSI requests and CSI reports atspecific resources in the time domain and to prevent degradation inthroughput. In the related art, a resource for a CSI report isallocated, such that an uplink data signal may not be allocated. Incontrast, in the second embodiment, with the above-described CSI reportinterval setting and resource allocation, the operation to transmit aCSI report with respect to a CSI request can be regarded as theretransmission operation of an arbitrary data signal, thereby minimizingconsumption of downlink control signals for uplink signal allocation.

Third Embodiment

In a third embodiment, a CSI request is transmitted from a transmissionapparatus to each reception apparatus to be temporally distributed atthe timing earlier than the transmission timing of the reference signalCSI-RS for CSI measurement. In this case, as a value indicating how manysubframes a CSI request is transmitted to each reception apparatusearlier than CSI-RS, a CSI report offset is set to differ among thereception apparatuses. Each reception apparatus sets the timing delayedby the CSI report offset after a predefined report interval elapses fromthe reception timing of CSI-RS as the CSI report timing of the ownapparatus on the basis of the CSI report offset. Each receptionapparatus calculates CSI from the reference signal CSI-RS, and transmitsthe CSI report to the transmission apparatus at the CSI report timing ofthe own apparatus. The CSI report offset can be acquired from thedifference between the reception timing of the CSI request and thereception timing of CSI-RS in the reception apparatus. The transmissiontiming of CSI-RS may be notified to the reception apparatus, and the CSIreport offset may be acquired from the reception timing of the CSIrequest and the transmission timing of CSI-RS by each receptionapparatus. The CSI report offset may be notified from the transmissionapparatus to each reception apparatus. Thus, the timing at which the CSIrequest is transmitted and the timing at which the CSI report istransmitted are respectively distributed.

FIG. 6 is a block diagram showing the configuration of a main part of atransmission apparatus according to a third embodiment of the invention.FIG. 7 is a block diagram showing the configuration of a main part of areception apparatus according to the third embodiment of the invention.In the figures, the same constituent elements as those in the firstembodiment are represented by the same reference numerals. Descriptionwill be mainly provided focusing on portions different from the firstembodiment, and description of the same portions will be omitted.

The transmission apparatus of the third embodiment includes a CSI reportoffset setting section 642, and the operation of a CSI request settingsection 637 is different from the first embodiment. The CSI reportoffset setting section 642 sets a different integer value for eachreception apparatus as a CSI report offset. The CSI report offsetsetting section 642 instructs a subframe earlier than the CSI-RStransmission timing received from the CSI-RS generator 138 by the CSIreport offset as the CSI request transmission timing to the CSI requestsetting section 637 on the basis of the set value of the CSI reportoffset. In the example of UE1 in FIG. 8 described below, the CSI requesttransmission timing is before 2 subframes. The CSI-RS generator 138notifies the CSI-RS transmission timing to each reception apparatusregularly through a notification channel or the like. The CSI reportoffset setting section 642 instructs the interval between the subframe,in which the CSI request is transmitted, and the subframe, in which theCSI report is transmitted, based on the value of the CSI report offsetto the separator 153 of the relevant UE. In the example of UE1 in FIG. 8described below, the subframe interval is 2×2=4 subframes.

The CSI request setting section 637 sends a notification to thescheduler 136 to generate a control signal of a CSI request for UE in asubframe of the indicated CSI request transmission timing of the CSIreport offset setting section 642. The separator 153 obtains informationregarding the CSI request transmission timing from the CSI requestsetting section 637, receives the value of the subframe interval fromthe CSI request to the CSI report from the CSI report offset settingsection 642, and recognizes the timing of a subframe in which the CSIreport is transmitted from the relevant UE. The separator 153 cuts theCSI report from the reception signal in the relevant subframe, andoutputs the CSI report to the CSI report demodulator 154.

The reception apparatus of the third embodiment includes a CSI reportoffset detector 723, and the operation of a feedback informationgenerator 719 is different from the first embodiment. The CSI requestdetector 216 receives a demodulated signal output from the MIMOdemodulator 215 as input, detects a CSI request signal, and notifies thedetection result to the CSI calculator 214 and the CSI report offsetdetector 723. When an indication that a CSI request signal is detectedis indicated from the CSI request detector 216, the CSI report offsetdetector 723 acquires the CSI report offset from the difference betweenthe separately notified CSI-RS transmission timing and the CSI requestreception timing. The CSI report offset detector 723 outputs the CSIreport offset set value to the feedback information generator 719. Inthe example of UE1 in FIG. 8 described below, the CSI report offset is 2subframes. In the CSI report offset detector 723, the CSI report offsetmay be calculated and acquired from the difference between the CSIrequest reception timing and the CSI-RS reception timing.

The feedback information generator 719 generates feedback informationincluding the CSI report value calculated by the CSI calculator 214 andoutputs the feedback information to the multiplexer 221. At this time,the feedback information generator 719 generates a signal as feedbackinformation in a subframe delayed by the CSI report offset set valuenotified from the CSI report offset detector 723 after a predefinedreport interval elapses from the reception timing of CSI-RS. Here, thepredefined report interval from the reception timing of CSI-RS is setto, for example, the number n_(CSI-RS) of subframes which is determinedfor the reason from the viewpoint of a CSI report due to the amount ofprocessing in the user equipment. If it is necessary to transmit thedecoding result (Ack/Nack) of downlink data in the relevant subframe,the feedback information generator 719 synthesizes the CSI report valueand the Ack/Nack information, and outputs the result to the multiplexer221.

Next, the operations of the transmission apparatus and the receptionapparatus in the third embodiment will be described in detail. FIG. 8 isa diagram showing an operation relating to a CSI request and a CSIreport in the third embodiment. Here, as in the first embodiment, a casewill be described where a CSI request is transmitted from a base station(eNB) serving as a transmission apparatus to two user equipments (UE1and UE2) serving as a reception apparatus, and a CSI report is returnedfrom each user equipment to the base station.

The transmission apparatus eNB outputs an instruction of a CSI requestto the reception apparatuses UE1 and UE2 to be distributed over thereception apparatuses at the timing earlier than CSI-RS by the userequipment transmission signal processor 131 m. At this time, in the CSIreport offset setting section 642, an integer value is set as the CSIreport offset for the relevant reception apparatus, and the CSI requestis transmitted in a subframe earlier than CSI-RS by the CSI reportoffset. A reception apparatus UE which meets the CSI request determinesthe set value of the CSI report offset from the subframe in which PDCCHincluding the CSI request is detected and the transmission timing ofCSI-RS notified previously, and specifies the CSI report subframe of theown apparatus.

In the example of FIG. 8, the transmission apparatus eNB instructs a CSIrequest to the reception apparatus UE1 in PDCCH earlier than CSI-RS by 2subframes, and the reception apparatus UE1 receives the CSI request. Ifthe CSI request is detected, the reception apparatus UE1 transmits a CSIreport to the transmission apparatus eNB using a subframe after thenumber (for example, n_(CSI-RS)) of subframes of a predefined reportinterval from the transmission timing of CSI-RS and 2 subframes.Similarly, the transmission apparatus eNB instructs a CSI request to thereception apparatus UE2 in PDCCH earlier than CSI-RS by 3 subframes, andthe reception apparatus UE2 receives the CSI request. The receptionapparatus UE2 transmits a CSI report to the transmission apparatus eNBafter the number of subframes of a predefined report interval from thetransmission timing of CSI-RS and 3 subframes. With the above-describedconfiguration, from the viewpoint of the transmission apparatus eNB, itis possible to distribute the downlink control channel PDCCH for a CSIrequest in the time domain, and also to distribute the uplink datachannel PUSCH which is allocated as a CSI report.

As described above, in the third embodiment, the timing at which the CSIrequest is transmitted from the transmission apparatus to each receptionapparatus is distributed at the timing earlier than CSI-RS on the basisof the CSI report offset set in each reception apparatus. The CSI reportis transmitted from each reception apparatus to the transmissionapparatus at the timing delayed by the CSI report offset after thepredefined report interval elapses from the transmission timing ofCSI-RS. Thus, as in the first embodiment, it is possible to suppressconcentration of CSI requests and CSI reports at specific resources inthe time domain and to prevent degradation in throughput.

Fourth Embodiment

In a fourth embodiment, a CSI request is transmitted from a transmissionapparatus to each reception apparatus to be temporally distributedsimultaneously with or earlier than the transmission timing of thereference signal CSI-RS for CSI measurement. Each reception apparatussets the timing delayed by a CSI report offset after a predefined reportinterval elapses from the reception timing of CSI-RS on the basis of theCSI report offset using a value uniquely determined by a parameterdepending on each reception apparatus. Each reception apparatuscalculates CSI from the reference signal CSI-RS, and transmits the CSIreport to the transmission apparatus at the CSI report timing of the ownapparatus. The CSI report offset can be calculated and acquired using acalculation expression set and notified in advance in the transmissionapparatus and the reception apparatus. Thus, the timing at which the CSIrequest is transmitted and the timing at which the CSI report istransmitted are respectively distributed.

FIG. 9 is a block diagram showing the configuration of a main part of atransmission apparatus according to a fourth embodiment of theinvention. FIG. 10 is a block diagram showing the configuration of amain part of a reception apparatus according to the fourth embodiment ofthe invention. In the figures, the same constituent elements as those inthe first embodiment are represented by the same reference numerals.Description will be mainly provided focusing on portions different fromthe first embodiment, and description of the same portions will beomitted.

The transmission apparatus of the fourth embodiment includes a CSIreport offset setting section 942 and a user equipment identificationinformation storage section 943, and the operation of a CSI requestsetting section 937 is different from the first embodiment. Here, anexample will be described where user equipment identificationinformation is used as the parameter depending on each receptionapparatus, and an identification number C-RNTI of a user equipment whichis provided when a reception apparatus belongs to the relevanttransmission apparatus is used as the user equipment identificationinformation. The CSI report offset setting section 942 defines acalculation expression for obtaining the CSI report offset from the userequipment identification information (identification number C-RNTI) inadvance. The calculation expression and the identification number C-RNTIare notified to each reception apparatus through a notification channelor the like. The CSI request setting section 937 sets the CSI requesttransmission timing to each reception apparatus, and notifies settinginformation of the CSI request transmission timing to the CSI reportoffset setting section 942 and each user equipment reception signalprocessor. The CSI request setting section 937 sends a notification tothe scheduler 136 to generate a control signal of a CSI request for UEin the subframe of the set CSI request transmission timing.

The CSI report offset setting section 942 receives the identificationnumber C-RNTI of the relevant reception apparatus from the userequipment identification information storage section 943, and sets theCSI report offset for each reception apparatus on the basis of thedefined calculation expression. The CSI report offset setting section942 instructs a subframe, in which a CSI report is transmitted, based onthe set CSI report offset and the CSI-RS transmission timing receivedfrom the CSI-RS generator 138 to the separator 153 of the relevant UE.

The reception apparatus of the fourth embodiment includes a CSI reportoffset setting section 1024, and the operation of a feedback informationgenerator 1019 is different from the first embodiment. The CSI requestdetector 216 receives a demodulated signal output from the MIMOdemodulator 215 as input, detects a CSI request signal, and notifies thedetection result to the CSI calculator 214 and the CSI report offsetsetting section 1024. The CSI report offset setting section 1024calculates and acquires a CSI report offset on the basis of theidentification number C-RNTI of the own apparatus using a calculationexpression separately notified from the transmission apparatus through anotification channel or the like. The CSI report offset setting section1024 outputs the calculated CSI report offset to the feedbackinformation generator 1019. In the example of UE1 in FIG. 11 describedbelow, the CSI report offset is 1 subframe.

The feedback information generator 1019 generates feedback informationincluding the CSI report value calculated by the CSI calculator 214 andoutputs the feedback information to the multiplexer 221. At this time,the feedback information generator 1019 generates a signal as feedbackinformation in a subframe delayed by the CSI report offset depending onthe user equipment notified from the CSI report offset setting section1024 after a predefined report interval elapses from the receptiontiming of CSI-RS. Here, the predefined report interval from thereception timing of CSI-RS is set to, for example, the number n_(CSI-RS)of subframes which is determined for the reason from the viewpoint of aCSI report due to the amount of processing in the user equipment. If thedecoding result (Ack/Nack) of downlink data is transmitted in therelevant subframe, the feedback information generator 1019 synthesizesthe CSI report value and the Ack/Nack information, and outputs theresult to the multiplexer 221.

Next, the operations of the transmission apparatus and the receptionapparatus in the fourth embodiment will be described in detail. FIG. 11is a diagram showing an operation relating to a CSI request and a CSIreport in the fourth embodiment. Here, as in the first embodiment, acase will be described where a CSI request is transmitted from a basestation (eNB) serving as a transmission apparatus to two user equipments(UE1 and UE2) serving as a reception apparatus, and a CSI report isreturned from each user equipment to the base station.

The transmission apparatus eNB notifies the calculation expression forobtaining the set value of the CSI report offset by the parameterdepending on each reception apparatus to a plurality of receptionapparatuses belonging to the own apparatus. Here, as the parameter, theidentification number C-RNTI which is provided when each receptionapparatus belongs to the relevant transmission apparatus is used. Thecalculation expression is, for example, mod(C-RNTI_x,TCSI-RS). Here,C-RNTI_x is the identification number which is provided for UEx, andTCSI-RS is the transmission interval of CSI-RS.

The transmission apparatus eNB outputs an instruction of a CSI requestto the reception apparatuses UE1 and UE2 to be distributed over thereception apparatuses at the timing earlier than CSI-RS by the userequipment transmission signal processor 131 m. At this time, the CSIrequest transmission timing to each reception apparatus may be set onthe basis of the CSI report offset for each reception apparatus or maybe arbitrarily set. A reception apparatus UE which meets the CSI requestcalculates the set value of the CSI report offset using the calculationexpression notified previously, and specifies the CSI report subframe ofthe own apparatus on the basis of the CSI report offset.

In the example of FIG. 11, the reception apparatus UE1 acquires 1subframe, which is the CSI report offset of the own apparatus, by thecalculation expression, and transmits a CSI report to the transmissionapparatus eNB using a subframe after the number (for example,n_(CSI-RS)) of subframes of the predefined report interval from thetransmission timing of CSI-RS and 1 subframe. Similarly, the receptionapparatus UE2 acquires 3 subframes which are the CSI report offset ofthe own apparatus, and transmits a CSI report to the transmissionapparatus eNB using a subframe after the number of subframes of thepredefined report interval from the transmission timing of CSI-RS and 3subframes. With the above-described operation, from the viewpoint of thetransmission apparatus eNB, it is possible to distribute the downlinkcontrol channel PDCCH for a CSI request in the time domain and also todistribute the uplink data channel PUSCH which is allocated as a CSIreport.

As described above, in the fourth embodiment, the timing at which theCSI request is transmitted from the transmission apparatus to eachreception apparatus is distributed at the timing simultaneously with orearlier than CSI-RS. The CSI report is transmitted from each receptionapparatus to the transmission apparatus at the timing delayed by the CSIreport offset after the predefined report interval elapses from thetransmission timing of CSI-RS on the basis of the CSI report offsetusing a value uniquely determined by the parameter depending on eachreception apparatus. Thus, as in the first embodiment, it is possible tosuppress concentration of CSI requests and CSI reports at specificresources in the time domain and to prevent degradation in throughput.

As described above, in this embodiment, the transmission subframe of thereference signal for channel quality measurement is associated with thetransmission subframe of the channel quality request, and the channelquality request is transmitted simultaneously with or before thereference signal and reflected in setting the transmission subframe ofthe channel quality report. Thus, it is possible to suppressconcentration of channel quality requests and channel quality reportsand to prevent degradation in throughput. Therefore, in a cellularsystem, it becomes possible to realize high-order MIMO of amulti-antenna system, coordinated multiple-point transmission andreception, and the like with satisfactory characteristics.

Fifth Embodiment

In a fifth embodiment, a CSI request is transmitted from a transmissionapparatus to each reception apparatus to be temporally distributedsimultaneously with or earlier than the transmission timing of thereference signal CSI-RS for CSI measurement. Each reception apparatusdetermines the CSI report timing of the own apparatus on the basis of aCSI report offset using a value uniquely determined by a parameterdepending on each reception apparatus. In this case, the CSI reporttiming of the own apparatus is set to the timing delayed by the CSIreport offset after a predefined report interval elapses from the timingat which 1 set of CSI-RS is received from a start point as themeasurement start point of CSI-RS according to the level of apropagation loss between the transmission apparatus and the receptionapparatus reported to the transmission apparatus by the own apparatusfrom among a plurality of CSI-RS. Each reception apparatus calculatesCSI from a plurality of reference signals CSI-RS, and transmits a CSIreport to the transmission apparatus at the CSI report timing of the ownapparatus. The CSI report offset can be calculated and acquired using acalculation expression set and notified in advance in the transmissionapparatus and the reception apparatus. Thus, the timing at which the CSIrequest is transmitted and the timing at which the CSI report istransmitted respectively are distributed.

FIG. 12 is a block diagram showing the configuration of a main part of atransmission apparatus according to a fifth embodiment of the invention.FIG. 13 is a block diagram showing the configuration of a main part of areception apparatus according to the fifth embodiment of the invention.In the figure, the same constituent elements as those in the firstembodiment are represented by the same reference numerals. Descriptionwill be mainly provided focusing on portions different from the firstembodiment, and description of the same portions will be omitted.

The transmission apparatus of the fifth embodiment includes a path-lossinformation demodulator 1255, a CSI report offset setting section 1244,and a path-loss information storage section 1245, and the operations ofa CSI-RS generator 1238 and a CSI request setting section 1237 aredifferent from the first embodiment. Here, an example will be describedwhere the CSI-RS generator 1238 transmits CSI-RS corresponding to aspecific antenna in each subframe using 2 continuous subframes, and apath-loss information is used as the parameter depending on eachreception apparatus. An example will be described where reference signalreceived power (RSRP) which is reported to the transmission apparatusfor determining the need for handover by the reception apparatus is usedas the path-loss information.

The CSI-RS generator 1238 transmits CSI-RS corresponding to Ant#0 toAnt#3 in the subframe of the earlier timing from among 2 continuoussubframes, and transmits CSI-RS corresponding to Ant#4 to Ant#7 in thesubframe of the later timing. The CSI report offset setting section 1244defines a threshold value for comparison with path-loss information toobtain the CSI report offset in advance. The threshold value is notifiedto each reception apparatus through a notification channel or the like.The CSI request setting section 1237 sets the CSI request transmissiontiming to each reception apparatus, and notifies setting information ofthe CSI request transmission timing to the CSI report offset settingsection 1244 and each user equipment reception signal processor. The CSIrequest setting section 1237 sends a notification to the scheduler 136to generate a control signal of a CSI request for UE in the subframe ofthe set CSI request transmission timing.

The path-loss information storage section 1245 receives and stores thepath-loss information received from the relevant user equipmentextracted by the path-loss information demodulator 1255. The CSI reportoffset setting section 1244 receives the path-loss information reportedfrom the path-loss information storage section 1245 to the relevantreception apparatus, and sets the CSI report offset for each receptionapparatus on the basis of the magnitude relationship with the definedthreshold value. The CSI report offset setting section 1244 instructs asubframe, in which the CSI report is transmitted, based on the set CSIreport offset and the CSI-RS transmission timing received from theCSI-RS generator 1238 to the separator 153 of the relevant UE.

The reception apparatus of the fifth embodiment includes a RSRPcalculator 1325 and a CSI report offset setting section 1326, and theoperation of a feedback information generator 1319 is different from thefirst embodiment. The RSRP calculator 1325 measures received power ofthe reference signal using the channel estimation value received fromthe channel estimator 213, and outputs the received power of thereference signal to the feedback information generator 1319 and the CSIreport offset setting section 1326 as RSRP. The CSI report offsetsetting section 1326 uses the threshold value separately notified fromthe transmission apparatus through a notification channel or the like,and acquires the CSI report offset calculated from the magnituderelationship with the measured RSRP. The CSI report offset settingsection 1326 outputs the calculated CSI report offset to the feedbackinformation generator 1319. In the example of UE1 of FIG. 14 describedbelow, the CSI report offset is 2 subframes.

Next, the operations of the transmission apparatus and the receptionapparatus in the fifth embodiment will be described in detail. FIG. 14is a diagram showing an operation relating to a CSI request and a CSIreport in the fifth embodiment. Here, as in the first embodiment, a casewill be described where a CSI request is transmitted from a base station(eNB) serving as a transmission apparatus to two user equipments (UE1and UE2) serving as a reception apparatus, and a CSI report is returnedfrom each user equipment to the base station.

The transmission apparatus eNB notifies the threshold value forobtaining the set value of the CSI report offset by the measuredpath-loss information of each reception apparatus to a plurality ofreception apparatuses belonging to the own apparatus. Here, RSRP is usedas the path-loss information.

The transmission apparatus eNB outputs an instruction of a CSI requestto the reception apparatuses UE1 and UE2 to be distributed over thereception apparatuses at the timing earlier than CSI-RS by the userequipment transmission signal processor 131 m. At this time, the CSIrequest transmission timing to each reception apparatus may be set onthe basis of the CSI report offset for each reception apparatus or maybe arbitrarily set. A reception apparatus UE which meets the CSI requestcalculates the set value of the CSI report offset using the thresholdvalue notified previously, and specifies the CSI report subframe of theown apparatus on the basis of the CSI report offset.

It is assumed that, in a state where the transmission apparatus eNB setsthe threshold value smaller than the maximum value of RSRP by 15 dB, itis measured in UE1 that the measured value of RSRP is a value (RSRPmaximum value-10 dB) greater than the threshold value, it is measured inUE2 that the measured value of RSRP is a value (RSRP maximum value-25dB) smaller than the threshold value, and the measurement results arereported to the transmission apparatus eNB. At this time, in UE1, sincethe value is greater than the threshold value, 1 set of CSI-RS (in FIG.14, 2 continuous subframes) with CSI-RS immediately after receiving aninstruction of a CSI request as a start point is measured. A CSI reportis transmitted to the transmission apparatus eNB using a subframe afterthe number of subframes (for example, NCSI-RS) of a predefined reportinterval from when 1 set of CSI-RS is measured and 2 subframes. Incontrast, in UE2, since the value is smaller than the threshold value, aset of CSI-RS (in FIG. 14, 2 subframes which are transmitted at aninterval) is measured with CSI-RS after CSI-RS transmission turns asideonce immediately after receiving the instruction of the CSI request as astart point. A CSI report is transmitted to the transmission apparatuseNB using a subframe after the subframes of the predefined reportinterval from when 1 set of CSI-RS is measured, as in UE1, and 2subframes.

With the above-described operation, from the viewpoint of thetransmission apparatus eNB, it is possible to distribute the downlinkcontrol channel PDCCH for a CSI request in the time domain, and also todistribute the uplink data channel PUSCH which is allocated as a CSIreport. In a user equipment which has RSRP information greater than apredefined threshold value, and performs high-speed data transmission ata higher rank, a plurality of CSI-RS can be received at as close timingas possible, and the influence of measurement delay when measuring in aplurality of subframes can be reduced at the time of transmission with ahigh rank. In a user equipment which has RSRP information smaller than apredefined threshold value, and performs data transmission at a lowerrank, the CSI report timing can be controlled assuming that delayaccompanied by measurement is allowable. That is, in this embodiment, itis possible to spatially the timing at which the CSI report istransmitted between a plurality of user equipments. As described above,according to the fifth embodiment, it is possible to distribute CSIrequests and CSI reports in the time domain without causing degradationin throughput.

Although an example has been described where CSI-RS is transmitted using2 continuous subframes, the invention is not limited thereto. It shouldsuffice that 1 set of definitions based on path-loss information can bedetermined uniquely using a plurality of CSI-RS transmission subframes.As a determination method, a prenotification may be made as notificationinformation, and the shortest interval when a plurality of CSI-RStransmission subframes are transmitted at irregular intervals may beregarded as a start point.

Although an example has been described where CSI-RS corresponding toAnt#0 to Ant#3 is transmitted in the subframe of the earlier timing fromamong 2 continuous subframes, and CSI-RS corresponding to Ant#4 to Ant#7is transmitted in the subframe of the later timing, the invention is notlimited thereto. CSI-RS may be transmitted using 2 subframes inaccordance with the even-numbered and odd-numbered Ant numbers.

Although an example has been described where RSRP is used as thepath-loss information, the invention is not limited thereto. A parameterindicating the reception quality of a reference signal, such asreference signal received quality (RSRQ), may be used.

Sixth Embodiment

In a sixth embodiment, a CSI request is transmitted from a transmissionapparatus to each reception apparatus to be temporally distributedsimultaneously with or earlier than the transmission timing of thereference signal CSI-RS for CSI measurement. Each reception apparatusdetermines the CSI report timing of the own apparatus on the basis of aCSI report offset using a value uniquely determined by a parameterdepending on each reception apparatus. In this case, a CSI report offsetis set in accordance with the difference between RSRP of a cell whichtransmits a CSI request and RSRP of a cell which transmits CSI-RS as ameasurement target from among CSI-RS transmitted from a plurality ofcells, and the CSI report timing of the own apparatus is set to thetiming delayed by the CSI report offset after a predefined reportinterval elapses from the reception timing of CSI-RS. Thus, the timingat which the CSI request is transmitted and the timing at which the CSIreport is transmitted respectively are distributed.

As an example of a system which transmits CSI-RS from a plurality ofcells and performs a CSI report, there is a system which performs datatransmission or interference control between a plurality of cells in acoordinated manner for a macro-diversity effect (a geographicallyseparated transmission point is utilized, and a link having a separatepath-loss is utilized) (called coordinated multiple-point transmissionand reception: CoMP). A cell as a CSI report target at that time may becalled a CoMP measurement set.

FIG. 15 is a block diagram showing the configuration of a main part of atransmission apparatus according to a sixth embodiment of the invention.FIG. 16 is a block diagram showing the configuration of a main part of areception apparatus according to the sixth embodiment of the invention.In the figures, the same constituent elements as those in the fifthembodiment are represented by the same reference numerals. Descriptionwill be mainly provided focusing on portions different from the fifthembodiment, and description of the same portions will be omitted.

In the transmission apparatus of the sixth embodiment, the operations ofa path-loss information demodulator 1555, a CSI report offset settingsection 1544, and a path-loss information storage section 1545 aredifferent from the fifth embodiment. Here, an example will be describedwhere two cells of a serving-cell (a cell in which a user equipmentneeds to receive PDCCH) and a target-cell (an arbitrary cell other thanthe serving-cell in the CoMP measurement set: a candidate cell in whicha user equipment does not need to receive PDCCH, but data allocation orinterference control is performed) respectively transmit CSI-RS, andpath-loss information is used as a parameter depending on each receptionapparatus. As in the fifth embodiment, an example will be describedwhere RSRP is used as the path-loss information.

The path-loss information demodulator 1555 outputs a plurality of piecesof path-loss information received from the reception apparatuses to thepath-loss information storage section 1545. The CSI report offsetsetting section 1544 receives the transmission timing of CSI-RS inadvance in each cell in a state where each reception apparatus reportspath-loss information. The CSI report offset setting section 1544receives the path-loss information of a cell as a CSI report target andthe own path-loss information from the path-loss information storagesection 1545, and sets the CSI report offset for each receptionapparatus on the basis of a value obtained by comparison (or by takingthe difference). The CSI report offset setting section 1544 instructs asubframe, in which a CSI report is transmitted, based on the set CSIreport offset and the CSI-RS transmission timing of the relevant cell tothe separator 153 of the relevant UE.

The reception apparatus of the sixth embodiment includes an RSRPcomparator 1627, and the operations of an RSRP calculator 1625 and a CSIreport offset setting section 1626 are different from the fifthembodiment. The RSRP calculator 1625 measures reference signal receivedpower using the channel estimation value received from the channelestimator 213, and outputs reference signal received power to thefeedback information generator 1319 and the RSRP comparator 1627 as RSRPof each cell. The RSRP comparator 1627 compares RSRP of a cell whichtransmits a CSI request and RSRP of another call, and outputs thedifference to the CSI report offset setting section 1626. The CSI reportoffset setting section 1626 uses a defined calculation table separatelynotified from the transmission apparatus through a notification channelor the like, and acquires a CSI report offset which is calculated fromthe difference in RSRP received from the RSRP comparator 1627. The CSIreport offset setting section 1626 outputs the calculated CSI reportoffset to the feedback information generator 1319. In the example of UE1in FIG. 17 described below, the CSI report offset is 2 subframes.

Next, the operations of the transmission apparatus and the receptionapparatus in the sixth embodiment will be described in detail. FIG. 17is a diagram showing an operation relating to a CSI request and a CSIreport in the sixth embodiment. Here, a case will be described where CSIrequests are transmitted from a base station (eNB) of a serving cellserving as a transmission apparatus and a base station (eNBx) of atarget cell serving as another transmission apparatus to two userequipments (UE1 and UE2) serving as a reception apparatus, and a CSIreport is returned from each user equipment to the base station.

The transmission apparatus eNB notifies a reference value for obtainingthe set value of the CSI report offset by the difference in path-lossinformation between the two cells measured by each reception apparatusto a plurality of reception apparatuses belonging to the own apparatus(FIG. 18). FIG. 18 is a table showing an example of a reference value ofa CSI report offset corresponding to a difference in path-lossinformation between two cells in the sixth embodiment. FIG. 18 shows areference value offset of an offset with respect to a difference diff inpath-loss information. Here, RSRP is used as the path-loss information.

The transmission apparatus eNB outputs an instruction of a CSI requestto the reception apparatuses UE1 and UE2 to be distributed over thereception apparatuses at the timing earlier than CSI-RS transmission ofthe target cell by the user equipment transmission signal processor 131m. At this time, the CSI request transmission timing to each receptionapparatus may be set on the basis of the CSI report offset for eachreception apparatus or may be arbitrarily set. A reception apparatus UEwhich meets the CSI request calculates the set value of the CSI reportoffset using the reference value notified previously, and specifies theCSI report subframe of the own apparatus on the basis of the CSI reportoffset. A specific example will be described below.

In a state where the transmission apparatus eNB sets the reference valueas shown in FIG. 18, it is measured in UE1 that the RSRP differencebetween the serving cell and the target cell is −3 dB, it is measured inUE2 that the RSRP difference is 5 dB, and the measurement results arereported to the transmission apparatus eNB. At this time, in UE1, thereference value of the offset is 0 from FIG. 18. For this reason, inUE1, a CSI report is transmitted to the transmission apparatus eNB usinga subframe after the number (for example, n_(CSI-RS)) of subframes ofthe predefined report interval from when CSI-RS is measured in thetarget cell immediately after receiving the instruction of the CSIrequest and 2 subframes. Meanwhile, in UE2, as shown in FIG. 18, anoffset of 2 subframes is added. For this reason, in UE2, a CSI report istransmitted to the transmission apparatus eNB using a subframe after thenumber of subframes of the predefined report interval from when CSI-RSis measured immediately after receiving the instruction of the CSIrequest, as in UE1, and 4 subframes.

With the above-described operation, from the viewpoint of thetransmission apparatus eNB, it is possible to distribute the downlinkcontrol channel PDCCH for a CSI request in the time domain, and also todistribute the uplink data channel PUSCH which is allocated as a CSIreport. In a user equipment which has a small difference in RSRP betweenthe serving cell and the target cell at present, and the resource of thetarget cell is easily allocated, the CSI report of the target cell canbe performed early. In a user equipment which has a large difference inRSRP between the serving cell and the target cell at present, and theresource of the target cell is not easily allocated, the CSI reporttiming can be controlled assuming that report delay is allowable. Thatis, in this embodiment, it is possible to distribute the timing at whichthe CSI report is transmitted over a plurality of cells and userequipments which perform coordinated multiple-point transmission andreception. As described above, according to the sixth embodiment, it ispossible to distribute the CSI requests and CSI reports in the timedomain without causing degradation in throughput.

Seventh Embodiment

In a seventh embodiment, an SRS instruction is transmitted from atransmission apparatus to each reception apparatus at the timing beforean SRS transmission subframe by n_(srs) or at the earlier timing. Here,n_(srs) is the minimum required number of subframes necessary from theSRS instruction to SRS transmission for the reason from the viewpoint ofgenerating an SRS signal due to the amount of processing in the userequipment, similarly to n_(CSI-RS). The SRS instruction is a requestwhich causes SRS for measuring channel quality information to betransmitted from a reception apparatus serving as a communication party.The set value of the SRS transmission subframe is a given subframeinterval, is set by, for example, the number of reception apparatuseswhich perform communication, or the like, and is notified from thetransmission apparatus to the reception apparatus using notificationinformation or the like.

FIG. 19 is a block diagram showing the configuration of a main part of atransmission apparatus according to a seventh embodiment of theinvention. In the figure, the same constituent elements as those in thefirst embodiment are represented by the same reference numerals.Description will be mainly provided focusing on portions different fromthe first embodiment, and description of the same portions will beomitted.

The transmission apparatus of the seventh embodiment is different fromthe configuration in the first embodiment in that an SRS subframesetting section 1921, an SRS instruction setting section 1922, aresidual data quantity storage section 1923, and an SRS detector 1924are provided.

The SRS subframe setting section 1921 sets an integer value, which is avalue common to a plurality of reception apparatuses belonging to theown apparatus, as an SRS transmission interval, notifies the set valueof the SRS subframe interval to the SRS instruction setting section 1922regularly, and notifies the set value of the SRS subframe interval toeach reception apparatus through a notification channel or the like. TheSRS instruction setting section 1922 acquires the residual data quantityof each reception apparatus from the residual data quantity storagesection 1923, and sets the SRS transmission timing in accordance withthe residual data quantity. Here, an example will be described where abuffer status report (BSR) which is data buffer information reported byreception apparatus to determine the need for allocating an uplinkresource in the transmission apparatus is used as the residual dataquantity. With regard to the residual data quantity, another piece oftransmission data, information relating to a buffer, or the like may beused.

The SRS subframe setting section 1921 notifies user equipment-specificLTE SRS setting information to an LTE user equipment and an LTE-A userequipment.

The SRS instruction setting section 1922 sets a threshold value forcomparison with BSR information for obtaining an offset to be providedto the SRS transmission timing in advance. The threshold value isnotified to each reception apparatus through a notification channel orthe like. The SRS instruction setting section 1922 sets the SRSinstruction timing to each reception apparatus, and sends a notificationto the scheduler 136 to generate a control signal of an SRS instructionfor UE in the subframe of the set SRS instruction timing.

The residual data quantity storage section 1923 receives and stores theBSR information (not shown) received from the user equipment. The SRSinstruction setting section 1922 receives BSR reported by the receptionapparatus from the residual data quantity storage section 1923, and setsthe SRS transmission timing for each reception apparatus on the basis ofthe magnitude relationship with the defined threshold value. The SRSinstruction setting section 1922 instructs a subframe, in which SRS istransmitted, based on the set SRS transmission timing and the SRSsubframe received from the SRS subframe setting section 1921 to theseparator 153 of the relevant UE.

The transmission apparatus notifies the reference value for obtainingthe set value of the SRS transmission timing by the reported residualdata quantity of each reception apparatus to a plurality of receptionapparatuses belonging to the own apparatus (FIG. 20). FIG. 20 shows anexample of a reference value of an SRS transmission timing correspondingto a residual data quantity in the seventh embodiment. FIG. 20 shows areference value delay of the transmission timing delay amount withrespect to a residual data quantity BSR index.

The SRS detector 1924 detects SRS of UE received from the separator 153to measure the channel quality of a propagation channel from thereception apparatus to the transmission apparatus, and outputs thechannel quality to the scheduler 136. The scheduler 136 performs atleast one of frequency scheduling and adaptive MCS control on the basisof the channel quality received from the SRS detector 1924 as schedulingrelating to a transmission signal.

The separator 153 separates a data part from a signal transmitted fromthe reception apparatus in accordance with scheduling, and outputs thedata part to the demodulator/decoder (not shown).

FIG. 21 is a block diagram showing the configuration of a main part of areception apparatus according to the seventh embodiment of theinvention. In the figure, the same constituent elements as those in thefirst embodiment are represented by the same reference numerals.Description will be mainly provided focusing on portions different fromthe first embodiment, and description of the same portions will beomitted.

The reception apparatus of the seventh embodiment is different from thefirst embodiment in that an SRS instruction detector 2141, an SRStransmission timing detector 2142, and an SRS generator 2143 areprovided. The SRS instruction detector 2141 receives a demodulatedsignal output from the MIMO demodulator 215 as input, detects an SRSinstruction signal, and notifies the result to the SRS transmissiontiming detector 2142. When the indication that the SRS instructionsignal is detected by the SRS instruction detector 2141 is indicated,the SRS transmission timing detector 2142 acquires the SRS transmissiontiming from the separately reported residual data quantity. The SRStransmission timing detector 2142 outputs the SRS transmission timing tothe SRS generator 2143. In the example of UE2 in FIG. 22 describedbelow, the SRS transmission timing is T_(sfc) subframes. The SRSgenerator 2143 generates an SRS signal using a transmitted power setvalue which is notified from the SRS transmission timing detector 2142or on a control signal indicating the SRS instruction signal.

Next, the operations of the transmission apparatus and the receptionapparatus in the seventh embodiment will be described supplementally.FIG. 22 is a diagram showing an operation relating to SRS instructionand SRS transmission in the seventh embodiment. Here, as in the firstembodiment, a case will be described where an SRS instruction istransmitted from a base station (eNB) serving as a transmissionapparatus to two user equipments (UE1 and UE2) serving as a receptionapparatus, and SRS is transmitted from each user equipment to the basestation.

The transmission apparatus eNB outputs an SRS instruction to thereception apparatuses UE1 and UE2 by the user equipment transmissionsignal processor 131 m. A reception apparatus UE which meets the SRSinstruction determines the SRS transmission timing from the subframe inwhich PDCCH including the SRS instruction is detected and the referencevalue of the SRS transmission timing corresponding to the residual dataquantity notified previously, and specifies a subframe in which the ownapparatus transmits SRS.

In the example of FIG. 22, the transmission apparatus eNB transmits anSRS instruction to the reception apparatus UE1 in PDCCH before the SRSsubframe by n_(srs) subframes, and the reception apparatus UE1 receivesthe SRS instruction. If the SRS instruction is detected, the receptionapparatus UE1 transmits SRS to the transmission apparatus eNB using asubframe after the number (for example, n_(srs)) of subframes of apredefined report interval from the relevant subframe. Similarly, thetransmission apparatus eNB transmits an SRS instruction to the receptionapparatus UE2 in PDCCH before the SRS subframe by the n_(srs) subframes,and the reception apparatus UE2 receives the SRS instruction. Thereception apparatus UE2 transmits SRS to the transmission apparatus eNBusing a subframe after the number of subframes of the predefined reportinterval from the transmission timing of the SRS instruction and T_(sfc)subframes. With the above-described operation, from the viewpoint of thetransmission apparatus eNB, it is possible to distribute the resource ofthe uplink data channel PUSCH which is allocated as SRS transmission.

As described above, in the seventh embodiment, SRS is transmitted fromeach reception apparatus to the transmission apparatus at the timingdelayed by the delay amount based on the residual data quantity afterthe predefined report interval from the transmission timing of the SRSinstruction. Thus, it is possible to suppress concentration of SRStransmission at specific resources in the time domain and to preventdegradation in throughput. In particular, at the time of scheduling ofuplink data, UE having a large residual data quantity can transmit SRSat the early timing, thereby reducing resource allocation for datatransmission and MCS control errors in UE having a large residual dataquantity.

Although an example has been described where the SRS instruction istransmitted at the timing before the SRS transmission subframe byn_(srs), the invention is not limited thereto. As in the firstembodiment, the timing at which an SRS instruction is transmitted may bedistributed at the timing before the SRS transmission subframe byn_(srs) or at the earlier timing, and SRS may be transmitted at thetiming delayed by the delay amount based on the residual data quantityafter the predefined report interval. Thus, the timing at which the SRSinstruction is transmitted and SRS transmission can be respectivelydistributed, thereby suppressing concentration of SRS instructions andSRS transmission at specific resources in the time domain and preventingdegradation in throughput. When the received quality is satisfactory andsignal energy necessary for an SRS instruction is small in UE belongingto the relevant base station, or the like, it is not necessary todistribute the timing at which an SRS instruction is transmitted, andonly distribution of SRS transmission may be performed.

Eighth Embodiment

In an eighth embodiment, the SRS signal transmission timing in theseventh embodiment is set in accordance with surplus transmission power.FIG. 23 is a block diagram showing the configuration of a main part of atransmission apparatus according to an eighth embodiment of theinvention. FIG. 24 is a block diagram showing the configuration of amain part of a reception apparatus according to the eighth embodiment ofthe invention. In the figures, the same constituent elements as those inthe seventh embodiment are represented by the same reference numerals.Description will be mainly provided focusing on portions different fromthe seventh embodiment, and description of the same portions will beomitted.

The transmission apparatus of the eighth embodiment includes a surplustransmission power storage section 2323, and the operation of an SRSinstruction setting section 2322 is different from the configuration inthe seventh embodiment. The SRS instruction setting section 2322acquires the surplus transmission power of each reception apparatus fromthe surplus transmission power storage section 2323, and sets the SRStransmission timing in accordance with the surplus transmission power.An example will be described where a power head room (PHR) which istransmission power information reported to a transmission apparatus by areception apparatus is used as the surplus transmission power. Withregard to the surplus transmission power, information relating toanother power control, or the like may be used.

The SRS instruction setting section 2322 sets SRS transmission power inaccordance with the set SRS transmission timing, and instructs the SRStransmission power to the scheduler 136.

The transmission apparatus notifies a reference value obtaining the setvalue of the SRS transmission timing by the surplus transmission powerreported by each reception apparatus to a plurality of receptionapparatuses belonging to the own apparatus (FIG. 25). FIG. 25 shows anexample of a reference value of an SRS transmission timing correspondingto surplus transmission power in the eighth embodiment. FIG. 25 shows areference value delay of a transmission timing delay amount with respectto surplus transmission power PH.

In the reception apparatus of the eighth embodiment, the operations ofan SRS transmission timing detector 2442 and an SRS generator 2443 aredifferent from the configuration in the seventh embodiment. When theindication that the SRS instruction signal is detected by the SRSinstruction detector 2141 is indicated, the SRS transmission timingdetector 2442 acquires the SRS transmission timing from the separatelynotified surplus transmission power. The SRS transmission timingdetector 2442 outputs the SRS transmission timing to the SRS generator2443. In the example of UE2 in FIG. 26 described below, the SRStransmission timing is T_(sfc) subframes. The SRS generator 2443generates an SRS signal using a transmission power set value notifiedfrom the SRS transmission timing detector 2442 or on a control signalindicating the SRS instruction signal.

Next, the operations of the transmission apparatus and the receptionapparatus in the eighth embodiment will be described supplementally.FIG. 26 is a diagram showing an operation relating to SRS instructionand SRS transmission in the eighth embodiment. Description will bemainly provided focusing on portions different from the seventhembodiment, and description of the same portions will be omitted. Areception apparatus UE which meets the SRS instruction determines theSRS transmission timing from the subframe in which PDCCH including theSRS instruction is detected and the reference value of the SRStransmission timing corresponding to the surplus transmission powernotified previously, and specifies a subframe in which the own apparatustransmits SRS.

In the example of FIG. 26, the reception apparatus UE2 transmits SRS tothe transmission apparatus eNB using a subframe after the number ofsubframes of the predefined report interval from the transmission timingof the SRS instruction and T_(sfc) subframes. With the above-describedoperation, from the viewpoint of the transmission apparatus eNB, it ispossible to distribute the resource of the uplink data channel PUSCHwhich is allocated as SRS transmission.

As described above, in the eighth embodiment, SRS is transmitted fromeach reception apparatus to the transmission apparatus at the timingdelayed by the delay amount based on the surplus transmission powerafter the predetermined report interval from the transmission timing ofthe SRS instruction. Thus, it is possible to suppress concentration ofSRS transmission at specific resources in the time domain and to preventdegradation in throughput. In particular, at the time of scheduling ofuplink data, US having small surplus transmission power can transmit SRSat the early timing, thereby reducing uplink data allocation delay andMCS control errors in UE having small surplus transmission power. Aconfiguration is made such that UE having large surplus transmissionpower perform transmission with large power by the delay amount, therebyreducing MCS control errors.

In the eighth embodiment, as in the first embodiment, the timing atwhich an SRS instruction is transmitted may be distributed at the timingbefore the SRS transmission subframe by n_(srs) or at the earliertiming, and SRS may be transmitted at the timing delayed by the delayamount based on the surplus transmission power after the predefinedreport interval. Thus, the timing at which an SRS instruction istransmitted and SRS transmission can be respectively distributed,thereby suppressing concentration of SRS instructions and SRStransmission at specific resources in the time domain and preventingdegradation in throughput. As in the seventh embodiment, when thereceived quality is satisfactory and signal energy necessary for an SRSinstruction is small in UE belonging to the relevant base station, orthe like, it is not necessary to distribute the timing at which an SRSinstruction is transmitted, and only distribution of SRS transmissionmay be performed.

Ninth Embodiment

In a ninth embodiment, the SRS signal transmission timing in the seventhembodiment is set in accordance with the status of a discontinuousreception (DRX) operation. FIG. 27 is a block diagram showing theconfiguration of a main part of a transmission apparatus according to aninth embodiment of the invention. FIG. 28 is a block diagram showingthe configuration of a main part of a reception apparatus according tothe ninth embodiment of the invention. In the figures, the sameconstituent elements as those in the seventh embodiment are representedby the same reference numerals. Description will be mainly providedfocusing on portions different from the seventh embodiment, anddescription of the same portions will be omitted.

The transmission apparatus of the ninth embodiment includes a DRX statusmanager 2723, and the operation of an SRS instruction setting section2722 is different from the configuration of the seventh embodiment. TheSRS instruction setting section 2722 detects the DRX status which ispredicted in each reception apparatus by the DRX status manager 2723.Specifically, when data allocation is not performed for a given periodin the past to the reception apparatus, a state where there is a highpossibility for the transition to the DRX status is detected. The SRSinstruction setting section 2722 instructs the separator 153 to separateSRS of the reception apparatus in an SRS subframe immediately aftersubframes corresponding to a DRX cycle indicating the cycle of DRXelapses from the set SRS transmission timing.

The reception apparatus of the ninth embodiment includes a DRXcontroller 2851, and the operation of an SRS transmission timingdetector 2842 is different from the configuration of the seventhembodiment. When the indication that the SRS instruction signal isdetected within the n_(srs) subframes before a subframe in which thetransition to the DRX status is done is indicated on the basis of acontrol signal from the DRX controller 2851, the SRS transmission timingdetector 2842 acquires an SRS subframe immediately after a DRX cycleelapses as the SRS transmission timing.

Next, the operations of the transmission apparatus and the receptionapparatus in the ninth embodiment will be described supplementally. FIG.29 is a diagram showing an operation relating to SRS instruction and SRStransmission in the ninth embodiment. Description will be mainlyprovided focusing on portions different from the seventh embodiment, anddescription of the same portions will be omitted. A reception apparatusUE which meets the SRS instruction determines the SRS transmissiontiming from the subframe in which PDCCH including the SRS instruction isdetected and the reference value of the SRS transmission timingcorresponding to the residual data quantity notified previously, andspecifies a subframe in which the own apparatus transmits SRS.

In the example of FIG. 29, the reception apparatus UE2 starts the DRXoperation after 2 subframes from the transmission timing of the SRSinstruction. SRS is transmitted to the transmission apparatus eNB usingan SRS subframe immediately after the time of the DRX cycle elapses fromthe number of subframes of the predefined report interval. With theabove-described operation, from the viewpoint of the transmissionapparatus eNB, it is possible to distribute the resource of the uplinkdata channel PUSCH which is allocated as SRS transmission.

As described above, in the ninth embodiment, SRS is transmitted fromeach reception apparatus to the transmission apparatus at the timingdelayed by the delay amount based on the status of the DRX operationafter the predefined report interval from the transmission timing of theSRS instruction. Thus, it is possible to suppress concentration of SRStransmission at specific resources in the time domain and to preventdegradation in throughput. In the reception apparatus UE immediatelyafter returning from the DRX operation, errors in the uplinktransmission timing can be easily corrected. Although an operationexample has been described where the length of the DRX cycle based onthe DRX status is used, the invention is not limited thereto. Forexample, SRS transmission timing control may be performed using a gapperiod based on the status of a measurement gap operation set formeasurement at different frequencies, which is shared by thetransmission apparatus and the reception apparatus.

In the ninth embodiment, as in the first embodiment, the timing at whichan SRS instruction is transmitted may be distributed at the timingbefore the SRS transmission subframe by n_(srs) or at the earliertiming, and SRS may be transmitted at the timing delayed by the delayamount based on the status of the DRX operation after the predefinedreport interval. Thus, the timing at which the SRS instruction istransmitted and SRS transmission can be respectively distributed,thereby suppressing concentration of SRS instructions and SRStransmission at specific resources in the time domain and preventingdegradation in throughput. As in the seventh embodiment, when thereceived quality is satisfactory and signal energy necessary for an SRSinstruction is small in UE belonging to the relevant base station, orthe like, it is not necessary to distribute the timing at which an SRSinstruction is transmitted, and only distribution of SRS transmissionmay be performed.

Although an example has been described where the serving cell and thetarget cell are different base station apparatuses, the invention is notlimited thereto, and the serving cell and the target cell may beoperated as a plurality of cells in the same base station apparatus.

Various changes or applications may be made to the invention on thebasis of the description of the specification and known techniqueswithout departing from the spirit and scope of the invention, and fallinto the scope of the appended claims. The constituent elements in theforegoing embodiments may be combined in various ways without departingfrom the spirit of the invention.

Although in the foregoing embodiments, description has been provided asto the antennas, the invention may also be applied to antenna ports. Anantenna port refers to a logical antenna which is constituted by one ora plurality of physical antennas. That is, an antenna port is notlimited to referring to one physical antenna, and may refer to an arrayantenna or the like having a plurality of antennas. For example, in LTE,while how many physical antennas constitute an antenna port is notdefined, an antenna port is defined as the minimum unit such that a basestation can transmit different reference signals. An antenna port may bedefined as the minimum unit for multiplying the weight of a precodingvector.

Although a case has been described with the foregoing embodiments as anexample where the invention is implemented with hardware, the inventioncan be implemented with software.

Each function block employed in the description of each of theaforementioned embodiments may be typically implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. LSI is adopted here butthis may also be referred to as IC, system LSI, super LSI, or ultra LSIdepending on differing extents of integration.

The method of circuit integration is not limited to LSI, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, the utilization of an FPGA(Field Programmable Gate Array) or a reconfigurable processor whereconnections and settings of circuit cells in an LSI can be reconfiguredis also possible.

With the advancement of semiconductor technology or other derivativetechnologies, if an integrated circuit technology comes out to replaceLSI, it is naturally also possible to perform function block integrationusing this technology. The application of biotechnology is alsopossible.

This application is based on Japanese Patent Application No.2009-133133, filed on Jun. 2, 2009, Japanese Patent Application No.2009-254160, filed on Nov. 5, 2009, and Japanese Patent Application No.2010-030237, filed on Feb. 15, 2010, the contents of which areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

The invention has an advantage of suppressing concentration of channelquality information requests and reports at the time of discontinuouslytransmitting reference signals at specific resources in a time domainand preventing degradation in throughput, and is useful as a wirelesscommunication apparatus, a wireless communication method, and the likewhich can be applied to a wireless communication system, such as acellular system.

REFERENCE SIGNS LIST

-   131 m, 131 n: user equipment transmission signal processor-   132: encoder/modulator-   133: precoding processor-   134 a to 134 d, 134 e to 134 h: transmission RF section-   135 a to 135 d, 135 e to 135 h: antenna-   136, 436: scheduler-   137, 637, 937, 1237: CSI request setting section-   138, 1238: CSI-RS generator-   139: LTE 4RS generator-   140, 440: CSI report interval setting section-   141: downlink control signal generator-   151 m, 151 n: user equipment reception signal processor-   152: reception RF section-   153: separator-   154: CSI report demodulator-   211 a, 211 b: antenna-   212 a, 212 b: reception RF section-   213: channel estimator-   214: CSI calculator-   215: MIMO demodulator-   216: CSI request detector-   217: decoder-   218: CRC checker-   219, 719, 1019, 1319: feedback information generator-   220: encoder-   221: multiplexer-   222: transmission RF section-   642: CSI report offset setting section-   723: CSI report offset detector-   942, 1244, 1544: CSI report offset setting section-   943: user equipment identification information storage section-   1024, 1326, 1626: CSI report offset setting section-   1245, 1545: path-loss information storage section-   1255, 1555: path-loss information demodulator-   1325, 1625: RSRP calculator-   1627: RSRP comparator-   1921: SRS subframe setting section-   1922, 2322, 2722: SRS instruction setting section-   1923: residual data quantity storage section-   1924: SRS detector-   2141: SRS instruction detector-   2142, 2442, 2842: SRS transmission timing detector-   2143, 2443: SRS generator-   2323: surplus transmission power storage section-   2723: DRX status manager-   2851: DRX controller

1. A communication apparatus comprising: circuitry, which, in operation,detects a request signal for requesting a transmission of a signal; anda transmitter, which, in operation, transmits the signal, upon detectionof the request signal, in a subframe which is configured to be specificfor the communication apparatus among a plurality of communicationapparatuses and which is one among a plurality of subframes, theplurality of subframes being common to the plurality of communicationapparatuses and being configured using a value common to the pluralityof communication apparatuses, wherein said transmitter, in operation,transmits the signal with a period that is specific for thecommunication apparatus among the plurality of communicationapparatuses, the period being from the detection of the request signalto a transmission of the signal.
 2. The communication apparatusaccording to claim 1, wherein said transmitter, in operation, transmitsthe signal at a time that is specific for the communication apparatusamong the plurality of communication apparatuses.
 3. The communicationapparatus according to claim 1, wherein said transmitter, in operation,transmits the signal in the subframe after a defined number of subframesor more from the detection of the request signal.
 4. The communicationapparatus according to claim 3, wherein the defined number of subframesis configured to be common for the plurality of communicationapparatuses.
 5. The communication apparatus according to claim 1,wherein said circuitry, in operation, detects the request signal, whichis transmitted at a time that is specific for the communicationapparatus among the plurality of communication apparatuses.
 6. Thecommunication apparatus according to claim 1, wherein said circuitry, inoperation, detects the request signal, which is transmitted on a controlchannel.
 7. The communication apparatus according to claim 1, comprisinga receiver, which, in operation, receives first information indicatingthe plurality subframes configured using the value that is common to theplurality of communication apparatuses and second information indicatingthe subframe configured to be specific for the communication apparatus.8. The communication apparatus according to claim 1, wherein thesubframes configured using the value that is common to the plurality ofcommunication apparatuses and the subframe configured to be specific forthe communication apparatus are configured using a period represented bya number of subframes.
 9. The communication apparatus according to claim1, wherein the subframes configured using the value that is common tothe plurality of communication apparatuses are subframes configured tobe specific for a cell.
 10. The communication apparatus according toclaim 1, wherein the signal is a sounding reference signal.
 11. Thecommunication apparatus according to claim 1, wherein the signal is asignal indicating channel quality.
 12. The communication apparatusaccording to claim 11, comprising a receiver, which, in operation,receives a reference signal with a period, which is represented by anumber of subframes, wherein said transmitter, in operation, transmitsthe signal indicating channel quality, which is computed based on thereference signal.
 13. The communication apparatus according to claim 12,wherein the reference signal is used for a communication systemcompatible with 8 antennas.
 14. The communication apparatus according toclaim 12, wherein the reference signal is a CSI reference signal.
 15. Acommunication method comprising: detecting a request signal forrequesting a transmission of a signal; and transmitting the signal, upondetection of the request signal, in a subframe which is configured to bespecific for a communication apparatus among a plurality ofcommunication apparatuses and which is one among a plurality ofsubframes, the plurality of subframes being common to the plurality ofcommunication apparatuses and being configured using a value common tothe plurality of communication apparatuses, wherein said transmittingincludes transmitting the signal with a period that is specific for thecommunication apparatus among the plurality of communicationapparatuses, the period being from the detection of the request signalto a transmission of the signal.